Discovery of 39Na

The new isotope ³⁹Na , the most neutron-rich sodium nucleus observed so far, was discovered at the RIKEN Nishina Center Radioactive Isotope Beam Factory using the projectile fragmentation of an intense ⁸Ca₄ beam at 3 4 5 MeV /nucleon on a beryllium target. Projectile fragments were separated and identified in flight with the large-acceptance two-stage separator BigRIPS. Nine ³⁹Na events have been unambiguously observed in this work and clearly establish the particle stability of ³⁹Na . Furthermore, the lack of observation of ^35,36Ne isotopes in this experiment significantly improves the overall confidence that ⁴Ne<₃ is the neutron dripline nucleus of neon. These results provide new key information to understand nuclear binding and nuclear structure under extremely neutron-rich conditions. The newly established stability of ³⁹Na has a significant impact on nuclear models and theories predicting the neutron dripline and also provides a key to understanding the nuclear shell property of ³⁹Na at the neutron number N =2 8 , which is normally a magic number.